MyMLH v4 Updates

[jonmarkgo]

Update omniauth-mlh to support MyMLH API v4

This PR updates the omniauth-mlh gem to support the new MyMLH API v4, replacing the previous v3 implementation.

Changes

• Updated API endpoints to use v4 instead of v3 (/v4/users/:id)
• Added support for new granular scopes system
• Updated data structure to match v4 response format
• Added comprehensive test coverage for v4 changes
• Bumped version to 2.0.0 for major API version change

Breaking Changes

1. The API endpoint has changed from /api/v3/user.json to /v4/users/:id
2. Implicit Grant flow has been removed (as per v4 specs)
3. New granular scopes system requires updates to scope configuration
4. Response data structure has been updated to match v4 format

Migration Guide

To migrate from v3 to v4:

1. Update your scope configuration to use the new granular scopes
2. Review and update any custom data parsing to match the new v4 response format
3. Ensure you're using the Authorization Code flow (Implicit Grant is no longer supported)

Testing

Added comprehensive test coverage for:

• New API endpoints
• Updated data structure
• Scope handling
• Error cases